Last year over 1,000 Australians died of skin cancer while two thirds of the Australian population will develop some form of skin cancer at some stage in their lives. This year it is anticipated that 150,000 Australians will go to their doctors for the examination and treatment of some form of sun induced skin cancer.
It is interesting to note that, in spite of public education campaigns and the widespread use of "Sun-Block" creams, skin cancer rates have not changed in recent years.
Even though there has been various sun protection aids in the market for many years, the present inventors have found that most consumers do not fully understand what an SPF rating means.
A typical fair skinned person, on a summers day in Australia, at noon (1:00 pm Eastern Summer Time), would "burn" in approximately 15 minutes (i.e. 0.25 hours). If this person applied "sun block" cream (or textile) of SPF 4 (if available), then this person would burn in 4 times 15 minutes, viz 1 hour. It is important to note, however, that this person would have received the same total UVR dose either way.
A common way of avoiding sunburn when performing activities in a sunny environment is to apply a sunburn cream to skin. The problem with such a solution however is that most sunburn creams only provide UVR protection up to an SPF rating of 15+ and therefore prolonged exposure to the sun can still cause damage to a persons skin despite the use of a sunburn cream.
In addition, avoiding exposure of skin to the sun by wearing clothing, for example a T-shirt, does not necessarily provide adequate UVR protection for the wearer, when the wearer is exposed to the sun for prolonged periods. This problem is compounded by the fact that in hot climates it is desirable to have light weight clothing, which typically has a low SPF rating.
For example, for materials having a density of less than 200 grams per square meter, nylon has an SPF rating of between 10 and 15, polyester has an SPF rating of between 13 and 17, wool has an SPF rating of 10-20 and cotton has an SPF rating of between 5 and 15. It follows therefore that a person wearing a shirt made of light weight fabric such as cotton or wool, if exposed to the sun for prolonged periods can still be subjected to significant doses of UVR radiation. Thus, over an extended period of time, a person working in the sun and wearing a cotton T-shirt can still be exposed to a significant cumulative dose of UVR radiation.
Essentially, the SPF protection of a fabric depends on the "Cover Factor" of the fabric. The Cover Factor may be defined as the percentage of the fabric surface that is covered by the yarns of the fabric. If one assumes that the yarns employed to weave or knit the fabric are completely opaque to UVR radiation (which is not the case in reality) then the fabric SPF would be simply related to Cover Factor by the following formula: ##EQU1##